Make some unit tests skip file system access

Make some unit tests skip file system access

Make unit tests for FileNameOptionManager not use the file system.
Introduce a FileInputRedirectorInterface to support mocking file
existence checks, and use a mock implementation in the tests.

These particular tests did quite a bit of file system access, and the
speedup is only a few ms, although significant percentually (something
like 80%).  But there can be tests where this has more effect, and this
approach provides a starting point for more work on eliminating
unnecessary file system access from the tests.

The main benefit is clearer and more robust test code, as it is no
longer necessary to construct actual files and ensure that they do not
conflict with other tests or cause issues if the test crashes or such.

Change-Id: Ib9a171331e988fa7e74b16078164f477f8296c6e